This invention relates generally to down hole tools and methods and apparatuses for manufacturing such items. More particularly, this invention relates to infiltrated matrix drilling products including, but not limited to, matrix drill bits, bi-center bits, core heads, and matrix bodied reamers and stabilizers, and the methods and apparatuses for manufacturing such items.
A matrix drill bit is typically fabricated using at least a graphite mold, a casting mandrel, or blank, positioned within the mold, and tungsten carbide matrix material placed within the mold and around the casting mandrel. The casting mandrel is typically much less expensive when compared to the cost of the tungsten carbide matrix material. According to one method for reducing the standard cost of matrix drill bit manufacturing, typically the diameter of the casting mandrel, or blank, is increased, thereby reducing the amount of expensive tungsten carbide matrix material used to form the drill bit casting. Thus, the thickness of the expensive tungsten carbide matrix material also is reduced.
However, increasing the diameter of the casting mandrel beyond a certain diameter causes problems with the drill bit manufacturing process. The thinner wall of matrix experiences intense pressure during the furnacing process due to the higher coefficient of thermal expansion of the steel casting mandrel, which oftentimes results in debilitating cracking in the final casting. This problem is especially prevalent when the junk slot displacements of the mold are directly milled into the graphite mold since graphite is essentially not compressible and is brittle. An ancillary problem is that the graphite mold can crack and leak due to the inability of the graphite matrix to accommodate the expansion pressure of the steel blank.
In view of the foregoing discussion, need is apparent in the art for improving the casting apparatus and/or the casting process so that the costs associated with casting fabrication are decreased. Additionally, a need is apparent for improving the casting apparatus and/or the casting process so that a smaller volume of tungsten carbide powder is used in the casting process. Further, a need is apparent for improving the casting apparatus and/or the casting process so that debilitating cracking in the final casting is eliminated or reduced. A technology addressing one or more such needs, or some other related shortcoming in the field, would benefit down hole drilling, for example fabricating castings more effectively and more profitably. This technology is included within the current invention.
The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments.